1. Field of the Invention
The present invention relates to a wire dot printing head for a serial printer, and more particularly to a wire dot printing head with a dot print missing prevention mechanism.
2. Description of the Prior Art
A conventional wire dot printing head has a mechanism wherein a wire fixing armature is supported operably by a biased leaf spring which is attracted to a core of an electromagnet against the elastic force of the leaf spring by a permanent magnet, and the armature is released by activating the electromagnet during a printing operation to cancel the magnetic flux from the permanent magnet. Generally, the wire dot printing head includes a printing wire guide which is formed of an oil impregnated felt material to prevent wear between printing wires and wire guiding elements.
When the conventional wire dot printing head is operated for a high duty printing operation, ie. for a relatively long period of time, the temperature of the wires increases. This causes oil to flow from the felt due to a decrease in the viscosity of the oil, and the oil passes through spaces between the printing wires because of capillary phenomena. The oil will leak into a space between a residual sheet and the biased leaf spring. As a result, sometimes this oil will cause the biased leaf spring to stick to the residual sheet. This can result in some dot-print operations not being performed.